1. Field
Collection of crude oil leaking from undersea oil wells.
2. General Background and State of the Art
In April 2010, an explosion on the Deepwater Horizon offshore drilling unit in the Gulf of Mexico lead to a massive oil spill. The well was about 5,000 feet (1,500 m) deep. By the time the underwater well was capped, about 4.9 million barrels of crude oil were released. From the initial leak to capping, about 53,000 barrels per day escaped.
Existing technology had great difficulty stopping the leak, probably for three reasons. First, leaks at almost a mile are difficult to reach and to act upon even if the capping process will work. Second, the oil is at very high pressure making any capping effort difficult. Third, damage to the wellhead structure left little with which to work.
At first, those working to stop the spill tried to use the existing blowout preventer. When that failed, most attempts to cap the well used mud or cement under high pressure to push against the high pressure of the escaping oil. After many tries using different approaches, the well was capped but not before millions of gallons of oil escaped during the long delays.
The Deepwater Horizon explosion and spill was not the first accident during undersea oil drilling. It likely will not be the last. Exploring, developing, and producing oil from undersea wells periodically results in an accidental leak leading to the unwanted loss of crude oil from the well facility. These ruptures cause the loss of crude oil leaking into the ocean and damage to marine and wetland environments.
A number of methods seek to stop the oil leak at its source. They include: (a) filling the sub-surface drilling pipe with drilling mud/cement to close the leaking pipe, (b) using explosives to close the leaking pipe and (c) drilling a “relief” well to relieve the leaking well pressure and direct the leaking crude oil to a new wellhead. Steel containers have been placed over the leak to attempt to connect a steel pipe to control the leak. However, as was evidence in the Deepwater Horizon incident, these methods were unable to respond promptly enough to prevent resulting environmental damage especially a mile below sea level.
The cost and complexity of mechanical recovery systems and the difficulty of deploying and installing such systems results in needless loss of crude oil and devastating damage to the marine and coastal environments. These mechanical systems attempt to cap and control the pressure of the leaking crude oil. This capping operation is extremely difficult in the deep/remote undersea environment. The operation not only requires the capping mechanism (mechanical capping block) but supporting equipment including hydraulic accumulators and manifolds necessary to control the pressure of the leaking crude oil.
Understandably, with more than 50,000 barrels of oil leaking every day and the oil slick growing in size, the well's owner were more concerned with stopping the leak than with containing the oil after it leaks from the well. Moreover, except for deploying booms to protect sections of the coast or around identifiable but relatively small slicks, little technology was available to collect most of the oil after it had leaked. However, a system that could contain already leaked oil would give those stopping the leak more time to act. In addition, as the oil flows out of the leak, the pressure may drop over time so that less oil continues to leak. The lower pressure may make stopping the leak easier. Therefore, if the leaking oil could be collected, stopping the leak over time may be made easier.
The figures are not to scale.